Acer negundo (boxelder)

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Intermountain Flora
Dioecious, wind-pollinated, soft-wooded tree mostly 5-12 m tall, the twigs in ours finely velutinous the first season, the pubescence sometimes persisting into the second or third season; leaves 3-foliolate, or sometimes some of them (especially on vigorous young shoots) pinnately 5- or 7-foliolate or even in part twice compound, the leaflets mostly 5-10 cm long and 2-5 cm wide, or wider when lobed, generally coarsely and often irregularly few-toothed, varying to subentire, or not infrequently with 1 or more rather shallow lobes (like enlarged teeth), in our finely short-hairy along the veins above and more conspicuously hairy across the surface beneath when unfolding, soon glabrate above, at maturity the pubescence on the lower side more or less confined to the vicinity of the axils of the main veins and sometimes also along the length of these veins, the central leaflet evidentaly stalked, on a petiolule mostly 5-25 mm long, the lateral ones more shortly stalked or subsessile; flowers produced with or a little before the leaves from axillary buds of the previous year, drooping on long, slender, often evidently spreading-hairy pedicels, the staminate in leafless umbelliform clusters, the pistillate in elongating, drooping racemes that are commonly subtended by a pair of new leaves; sepals mostly 4 or 5, minute, mostly 1-1.5 mm long or in pistillate flowers; ovary glabrous or often somewhat hairy, wanting from the staminate flowers, the stigmatic branches elongate, commonly 5-8 mm long, papillate all around; fruit in ours glabrous or with a few hairs on the thickened, seed-containing part, the mericarps of the samara each 2-3.5 long, spreading at a right angle or less; 2n = 26.

Cronquist, A., Holmgren, N.H., and Holmgren, P.K. (1997) "Intermountain Flora" pg. 312, vol. 3 part A, The New York Botanical Garden New York.